The goals of this study are: (1) to examine the effects of the calcium channel blocker, amlodipine, on the cardiovascular, hormonal, and psychoactive effects of oral methamphetamine, and (2) examine the effects of amlodipine on the metabolism and disposition kinetics of methamphetamine. The GCRC will be used for intravenous infusions, monitoring, and a controlled, safe inpatient setting which precludes the possibilities of other drugs being introduced which might invalidate the procedures of the study.